This invention relates to assembly machines and, more particularly, to automated machines adapted to assemble articles of manufacture made up of a plurality of parts.
Assembly machines of the type disclosed have been found suitable to assemble articles made up of several relatively small parts. Vibratory hoppers typically feed article parts to a movable turret. Some of the most successful units are those which incorporate a rotary turret including a plurality of spaced fixtures or nests adapted to receive the article parts from the hopper. As each article part is received, the turret is intermittently rotated or indexed, thus presenting an empty nest to the feed hopper at predetermined timed intervals. The indexing turret is ordinarily in a horizontal plane but the machine could also be designed to operate at any other angle through the provision of suitable nests.
Assembly machines with rotary indexing turrets typically include at least one reciprocable plate mounted above the turret, substantially parallel thereto. The plates are mounted to a central movable shaft, which is either designed to reciprocate as in U.S. Pat. No. 3,143,792 or to rotate as in U.S. Pat. Nos. 3,065,530 and 3,939,544. The rotary shafts include cylindrical cams which translate rotation into reciprocation, as shown in the above patents.
In a typical operation an article part is fed by a hopper to the assembly turret where it is received at a nest. The turret is then indexed to a work station where any number of operations may be performed. For example, a second hopper may be utilized to provide a second part which can be secured to the article part at the work station. Alternatively or additionally the article part can be drilled, tapped, relocated, stamped or removed from the turret. Any number of other conventional operations can also be performed. In certain applications it may be desirable to include a probe at the second station to insure that the article part has been properly positioned on the nest.
The plates, which are often referred to as tool plates, are designed to support tooling which may take the form of tools, tool activators, or the like. When a machine is provided with two tool plates, tools may be mounted to one plate, with means for actuating the tools mounted to the second plate. Thus, as the tool plates reciprocate with respect to the turret, operations are performed on the article parts.
Regardless of the exact configuration of the tool plates and their tooling, it is imperative that the indexing of the turret be synchronized with the reciprocation of the tool plates. Otherwise, the turret might be indexing while operations are being performed at a work station, thereby resulting in jamming or damage to the article parts and/or the tooling. Synchronization has conventionally been implemented by powering the turret and the tool plates off of the same drive shaft as taught in U.S. Pat. Nos. 3,065,530 and 3,939,544. By mechanically interlocking the indexing and operation components of the machine in this manner, full synchronization is assured. At the same time, a relatively simple drive mechanism is made possible.
While the above-described designs have been generally acceptable, the mechanical interlock between the indexing and operation portions of the machines does give rise to certain limitations. For example, in a machine with a rotary tool plate drive shaft, the shaft must be continuously rotating when intermittent indexing is taking place.
In many automated assembly operations it has been found that dwells must be provided at certain portions of the cycle of reciprocation of the tool plates. For example, to insure that the tooling is in a retracted position while the turret is indexing, it may be desirable to provide a dwell period while the tool plates are in their uppermost position. An example of this type of cycle is shown and explained in U.S. Pat. No. 3,065,530. A dwell period is also ordinarily necessary during the time in which an article part is moving from the feed hopper to the escapement. The term "escapement" as used herein is intended to define means for gripping the article parts when they are being transferred from the hopper to the turret nest. This dwell is also shown in the aforementioned patent. Conventional "pick-up and place" operations performed on assembly machines such as those described in U.S. Pat. Nos. 3,231,968 and 3,939,544 also ordinarily require a tool plate dwell period while the article parts are transferred from the hopper to the pick-up device.
As mentioned above, each tool plate is typically driven by a cylindrical cam mounted to the tool plate drive shaft. The tool plate dwells discussed above are provided by horizontal portions in the cam. Thus, with the tool plate drive shaft and the cam making one rotation for each machine cycle, the tool plate reciprocation of each cycle must be concentrated into the remaining portion of the cam. For example, if the dwell period must comprise 1/4 or 90.degree. of a cycle, the reciprocation must be provided within the remaining 270.degree.. The resulting steep cam contours can cause excessive friction and bring about loading difficulties unless severe weight limits are put on the components mounted to the tool plates.
A similar situation pertains to the conventional turret drive train. The turret is typically driven by a cross over cam which acts on a follower mounted to the underside of the turret as shown and described in U.S. Pat. No. 3,143,792. In order to provide an intermittent indexing motion, the cross over cam must include flat portions along much of its surface. The portion of the cam which actually indexes the turret must therefore have a relatively steep contour, thus causing high friction and loading difficulties discussed above with respect to the tool plates.
A primary object of the present invention is to overcome the above difficulties while providing a machine which is relatively simple in construction.